Project Summary/Abstract Lung transplant (LT) is an option for advanced lung diseases; unfortunately, due to post-transplant complications, both infections and non-infections (i.e., rejections), which leads to chronic lung allograft dysfunction (CLAD) it is only a treatment and not a cure. The hallmark of CLAD is the displacement of normal epithelium by a relentless deposition of extracellular matrix. Currently, there are no effective therapies for the prevention or treatment of CLAD. This proposal will use both a novel mouse orthotopic-transplant-with-regrafting to model the pathobiology of CLAD and human translational studies to evaluate mechanisms that lead to epithelial progenitor cell (EPC) loss and fibrogenesis during CLAD. We have previously shown that a type 1/17 inflammatory environment promotes acute rejection (AR), while the type 2 fibroproliferative environment supports the development of fibrosis in CLAD. Our preliminary data suggests that loss of epithelial progenitor cell reserves (EPCR) leads to fibroplasia and CLAD. Additionally, we propose that IL-22, in part through a p53-dependent pathway, functions differently at different stages post-transplantation. During the early stages of allograft injury, IL-22 is beneficial by promoting EPCR expansion. However, later on, IL-22 influences fibroblasts thereby stimulating the development of fibrosis in CLAD. The consequence of IL-22 upon the lung allograft depends on the cell type on which its receptor is expressed. During the inflammatory type 1/17 phase, the EPCR expresses the heterodimeric IL-22 receptor (IL-22R1 and IL-10R2), while fibroblasts do not. Thus, during early injury stages post-LT, IL-22 mediates downregulation of p53 signaling just in epithelial cells, thereby allowing progenitor cells to proliferate and regenerate the lung epithelium. Conversely, when continued insults to the lung allograft leads to a fibroproliferative type 2 environment, the IL-22 receptor expression is induced on fibroblasts and reduced on EPCR. Thus, at this later stage, IL-22 interacts preferentially with its receptor on fibroblasts, skewing them towards an invasive, fibrotic phenotype resulting in CLAD. Our preliminary pre-clinical data in murine models suggest that manipulating IL-22 and p53 can affect the outcome of CLAD, either protective via promotion of EPC regeneration or harmful via promotion of fibroplasia. Moreover, we will insure the relevance of these pathways in humans using lung transplant (LT) recipients biological samples that include BALF protein and cultured fibroblasts as well as brushing of the allograft airway epithelial cells.